Generally, as shown in FIG. 1 of the accompanying drawings, the exhaust system of a diesel engine has a structure in which a cylinder head 10 and an exhaust manifold 12 are separately assembled, and the exhaust manifold 12 is mainly formed of an expensive Steel Use Stainless (SUS) material to endure a thermal load due to high-temperature exhaust gas. Also, the exhaust manifold 12 usually has a weight of 3 kg or more.
Recently, in view of the high oil price trends and the regulation reinforcement policies of exhaust gas, reducing the weight of the engine development is an important factor. To this end, engine components need to be modularized into one, or the development of new lightweight materials is needed.
As an example of achieving reduced weight by modularizing the engine components into one, the exhaust manifold 12 is being integrally manufactured with the cylinder head 10.
As shown in FIG. 2, in case of the exhaust manifold integrated cylinder head, the exhaust manifold 12 forming an exhaust port 14 is integrally formed with the cylinder head 10. A separate exhaust diffuser 16 for mounting a turbocharger is coupled to an outlet terminal of the integral exhaust manifold 12.
In this case, the outlet terminal (joining part) of the exhaust port of the exhaust manifold integrally formed with the cylinder head extends toward the diffuser 16. The shape of the diffuser has a vertical bent pipe to upwardly discharge exhaust gas from the exhaust port. Accordingly, the exhaust gas discharged from the diffuser 16 flows to the turbocharger connected to the upper side of the diffuser 16.
However, as shown in FIG. 3, which illustrates a simulation result of the pressure and the speed distribution of exhaust gas, since the typical diffuser 16 is disposed vertical to the exhaust port 14 of the exhaust manifold 12 integrally formed with the cylinder head 10, a rapid flow change occurs at a point where the diffuser 16 is connected to the exhaust port 14, thereby causing a flow stagnation of exhaust gas.
That is, since the exhaust port and the diffuser are almost perpendicular to each other when exhaust gas flows from the exhaust port of a horizontal array to the diffuser of a vertical array, an orthogonally bent portion acts as a flow resistance, thereby causing the flow stagnation of exhaust gas and thus reducing the flow coefficient of exhaust gas.
Also, as the diffuser is separately coupled to the outlet terminal (joining part) of the exhaust port of the exhaust manifold integrally formed with the cylinder head, the weight of the diffuser and cylinder head and the man-hours of manufacturing the diffuser and cylinder head may increase.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the inventive concept and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.